Heretofore, mechanical rotary vane and piston type pumps capable of producing intermediate pressures (0.01 to 10 Torr) have been used as backing pumps for oil diffusion and turbomolecular pumps as well as roughing pumps for starting ion pumps and cryogenic pumps. These pumps are generally quite heavy, bulky and usually produce oil vapors which can contaminate a vacuum system. Such pumps require relatively large amounts of electrical power.
Presently, the most commonly used backing or roughing pumps are oil-sealed rotary mechanical pumps. The smallest commercially available oil-sealed rotary mechanical pump has a mass of approximately 8 Kg, a volume of approximately 7 liters, and an power requirement of approximately 300 Watts. As indicated above, such pumps are disadvantageous in high vacuum applications because they can inadvertently allow some oil vapor to back-stream into high vacuum pumps and chambers, especially if a power failure should occur. In addition, such pumps are subject to oil leakage during shipment and storage.
Diaphragm pumps have been used as oil-free pumps to produce intermediate pressures down to 1 Torr. By careful selection of pump design, including multiple stages of pumping, one can achieve pressures of less than 20 Torr using very low power consumption (less than 4 Watts), low-mass (less than 0.5 Kg) pumps such as the Brailsford Model TD4X2, (4 pump heads in series, with a 4.5 mm stroke). The lowest pressures obtainable with such a pump design appears to be limited by the minimum pump head dead volume, and the gas pressure required to open the rubber leaf-type pump valves which are utilized.
Portable instrumentations requiring the use of intermediate vacuum pumping have generally relied upon the use of heavy and bulky mechanical pumps including oil-sealed rotary pumps which have the inherent disadvantages noted above.
The present invention relates to a miniature mechanical pump which is an improvement over prior art mechanical pumps.